PURPOSE: There is a lack of clinical evidence supporting the use of lavage in patients with peritonitis. It is known that fluids such as normal saline cause temporary damage to the peritoneum and that increased production of proinflammatory mediators is associated with a poor outcome. This study used an experimental model to evaluate the effect of lavage on the peritoneal mesothelium and the ability of peritoneal mesothelial cells to produce a battery of proinflammatory mediators (TNF alpha, IL-1 beta, GRO alpha, and ICAM-L). METHODS: Wistar rats were allocated into four groups (control, peritonitis, lavage, peritonitis plus lavage). Peritonitis was induced by exposure to zymosan and saline was used for lavage. After 18, 24, and 43 hours, mesothelial imprints were taken from the peritoneum for histology, serniquantitative reverse transcription-polymerase chain reaction, Western blot analyses, and immunocytochemistry.RESULTS: Both peritonitis and lavage caused peritoneal damage at 18 and 24 hours, and this effect was additive. At varying times, peritoneal mesothelial cells from animals undergoing lavage had greater up-regulation (P < 0.05) of mRNA expression for TNF alpha, IL-1 beta, GRO alpha, and ICAM-I and greater production (P < 0.05) of TNF alpha, IL-1RII, GRO alpha, and ICAM-I. The latter was heavily concentrated at the cell membrane.CONCLUSIONS: Lavage causes self-limiting peritoneal damage and this is associated with an up-regulation of proinflammatory mediators in animals with peritonitis.